1. Field of the Invention
The present invention relates generally to a sheet transport apparatus. More particularly, the present invention relates to a sheet transport apparatus for use in a copying machine, scanner, printer, facsimile machine, microfilmer, and the like.
2. Description of the Prior Art
Copying machines, printers and facsimile machines are used in a wide variety of applications. A mechanism for transporting sheets of paper is essential for such machines.
A sheet transport apparatus used in such machines includes two relatively-positioned rollers, or a belt and a roller, for nipping a sheet of paper to be transported. Such rollers, or the belt and roller, rotate together to transport the sheet of paper.
FIG. 2 shows such a conventional sheet transport apparatus in which a pair of rollers are nipping a sheet of paper 10. A soft roller 12 is made of a material, such as rubber having a high coefficient of friction, and is connected to a drive source, e.g., a motor, so that soft roller 12 serves as a drive roller. In a position relative to soft roller 12 there is provided a hard roller 14 made of synthetic resin or the like. Typically, soft and hard rollers 12, 14 apply an appropriate nipping force therebetween to thereby increase the force of transporting sheet 10. In other words, a certain pressure is applied to a nipping area where sheet 10 is nipped between soft and hard rollers 12 and 14, respectively.
Thus, soft and hard rollers 12, 14 of the conventional sheet transport apparatus apply a high pressure to sheet 10, so that the nipping area of sheet 10 is pressed with a given pressure. In the meanwhile, an area of the sheet 10 other than the nipping area remains free from pressure. As a result, there is generated a difference in pressure between the nipping area and the free area, which causes distortion to be developed on the inside of sheet 10. This distortion disadvantageously leads to so-called "transportation wrinkles" which are indicated by arrow 16 in FIG. 2.